Skip to main content

Full text of "Practical Organic Chemistry"

See other formats

APPENDIX                                     253

acid into the acid chloride. Bromine in presence of phosphorus
forms in the same way, first, the acid bromide, and in the
second stage of the reaction, the bromine substitution product.
The bromine in all cases attaches itself to the a-carbon (z>.,
next the carboxyl). Where no free hydrogen exists in this
position, as in trimethylacetic acid, no substitution occurs.
Iodine can be introduced by the action of KI on the bromine


Monohalogen derivatives may also be obtained from the
unsaturated acids by the action of the hydracids (HC1, HBr,
HI). In this case the halogen attaches itself to the carbon
farthest from the carboxyl. Thus acrylic acid gives with HBr
the /3-bromopropionic acid,

rilo-.CII.CO.OII   !   HI5r~CII.jlir.CILj.COOH.

The action of the hydracids, PClr, andPI3r5, on the hydroxy-
acids also yields the halogen derivatives,

riI:1.CI!(OiI).CO()II -I   HBr. = CILj.CIIBr.COOH + HaO.

au<:ii(<>ii).coon >i 2pci, = cn,.cnci.coci + 2?6ci,


In the latter case the acid chloride must be subsequently
decomposed by water to obtain the acid.

The increase in the number of halogen atoms in the acid
raises the boiling point as well as the strength of the acid as
determined by its dissociation constant K.

15.1'.                            K.

Act-tic ucid.......     118           '0018

Monochlonvct'lie acid   .   .   .      185           "155

Diclilorucctic ucid.....      190         5*14

Trichloracctic ucid   ....      195      121

Some of the transformations of monohalogen acids are
illustrated by the following equations :

CII.,n.<'<><)! I   t   II.jO          (.'ILjOH.COOII -i   I1CL

CILCl.COOIl   I   KCN    ~ CHyCN.COOII -I   K.C1
CIIoCl.C'OOII   !   2NH:,   - CIIyNIUCOOlI   I   N1I4CL

C'U.,Iir.C(.'K)II   I   Ag..      -=--    |    "             + 2AgBr
T  KOII - CII2":CI1.COOH + KI + H2O.